Time-Resolved Resonance Raman and Density Functional Study of an Azirine Intermediate in the 2-Fluorenylnitrene Ring-Expansion Reaction To Form a Dehydroazepine Product

摘要

We report time-resolved resonance Raman spectra for the azirine intermediate produced in the 2-fluore-nylnitrene ring-expansion reaction to form a dehydroazepine product. The/Raman bands obtained with a 252.7 nm probe wavelength and 500 ns delay time exhibit reasonable agreement with predicted vibrational freuencies from density functional calculations for two isomers of azirine intermediates that may be formed from a 2-fluorenylnitrene precursor. The Raman bands observed por delay times of 15 ns and 10 mus were consistent with predicted vibrational frequencies from density functional calculations for the 2-fluorenylnitrene and dehydroazepine product species as well as previously reported 416 nm time-resolved Raman spectra obtained on the ns and mus time scales. Our results demonstrate that the 2-fluorenylnitrene ring-espansion reaction to produce dehydroazepine products proceeds via relatively long-olived 2-fluorenylnitrene and azirine intermediates. Substitution of a phenyl ring para to the nitrene group of phenylnitrene appears to lead to significant changes in the ring-expansion reaction so that longer lived arylnitrene and azirine interrmediates can be ob-served. This should enable the chemical reactivity of azirine intermediates formed from arylnitrenes to be examined more readily.